1. Field of the Application
The subject application relates to the compressor stator of an axial turbomachine. More particularly, the invention relates to a blade-retaining member for an axial turbomachine compressor stator. The invention relates also to an axial turbomachine.
2. Description of Related Art
In order to guide an annular flow, an axial turbomachine is fitted with coaxial shells defining the inside and outside of the flow. In a stator, internal shells are essentially connected to the inner ends of the stator blade. They form cylindrical walls having openings through which the stator blade tips are inserted so as to anchor them.
To increase the seal between an inner shell and the rotor, stators have a layer of abradable material applied to their internal shells, and the rotors have corresponding lip seals. During the operation of the turbomachine, the rotor moves and deforms so that the radial ends of the lip seals graze the corresponding abradable layers. They etch annular grooves which thus create labyrinth seals.
The inner ends of the blades extend into the layers of abradable material and are anchored there. They have openings in the layers of abradable material in which the retaining members are located.
These improve the radial retention of the blades in the shell. The lifetime of such a stator is improved as the anchoring thus produced is no longer dependent only on the bond between the blade and the abradable material. In the event of shock, ingestion or a fan blade detaching, the stator blades will beneficially stay firmly attached to their inner shell.
Patent EP 1213483 B1 discloses a stator stage in which the blade ends are connected in pairs by retaining and stiffening pieces. These are V-shaped and are inserted into cut-outs formed in the ends of the blades. When inserted, the arms of the V are folded so that their ends can fit into the cut-outs. However, this method of assembling requires that the assembling member is very long along the stator's major axis. This configuration may be incompatible with some internal stator shells which are narrow. The installation of such retaining pieces requires great precision to manually position each end of the branches of the V in the corresponding openings. After mounting, the tip of the V may project from the layer of abradable material in which it is supposed to stay embedded.
Patent EP 1626163 A2 has a blade retention clip in a shell of a rotating machine. The clip is inserted into a cut-out formed at the end of a blade and is embedded in a layer of abradable material applied to the inside of the shell. The clip forms a rectangular plate with a deformable L-shaped side member. The free end thereof has a hook engaging with a narrow strip of the blade material. On the side opposite the hook this narrow strip of material engages with a notch in the clip body. This clip effectively fixes a blade to a shell. However, it necessarily requires an elastic material for its implementation. In addition, it has a large axial dimension so as to be able to deform and to be mounted on the blades with a large pitch angle. This type of clip also demands high precision during assembly so that it takes the correct line for the hook to engage properly. The engaging movement of the hook must be gentle so as not to damage the elastic element because of its thinness. The combination of the cut-out and the hook on the lateral elastic element does not enable the clip to be firmly locked in a given direction. During the operation of applying the abradable material, the clip can pivot and project from the layer of abradable material, especially when its covering thickness is reduced.
A blade retaining plate which includes a folding finger is also known to a person skilled in the art. This plate is intended to be inserted into the holes of two adjacent blades, the finger extending therebetween. To ensure retention, this finger is folded towards the plate against one of the blades. To bend the finger carefully requires some degree of precision. This finger is particularly thin, which weakens it. Also, the finger points outward. The position of its tip is not controlled and it can pass through an annular layer of abradable material. By so protruding, it may contact the rotor lip seals.
Although great strides have been made in the area of compressor stators of axial turbomachines, many shortcomings remain.